WASHINGTON — The Obama administration and House Democrats said Monday they were undecided about whether to take part in or boycott an election-year investigation by Republicans into the Benghazi attack that killed four Americans.

House Speaker John Boehner announced last week he would create a select committee to examine the response to the deadly Sept. 11, 2012, assault on the U.S. diplomatic post in Libya that killed Ambassador Chris Stevens and three other Americans. Legislative aides said a vote to authorize the panel is expected sometime this week. On Monday, Boehner said Rep. Trey Gowdy, R-S.C., would head the investigation.

The action puts President Obama’s team and House Democrats in a bind. They are concerned about what they believe will be a partisan forum for attacks on the president and his top aides ahead of crucial midterm elections in November, which could swing the Senate to GOP control. But avoiding the committee altogether means sacrificing the ability to counter Republican claims.

White House press secretary Jay Carney stressed Monday that the administration always cooperates with “legitimate” congressional oversight — including sending witnesses to hearings and providing bipartisan committees with documents. He declined to characterize whether the Obama administration would view a House select committee as legitimate or illegitimate. But he said that what Republicans have said about the committee “certainly casts doubt” about its legitimacy.

Carney also suggested the select committee was unnecessary. “One thing this Congress is not short on is investigations into what happened before, during and after the attacks in Benghazi,” he told reporters.

Boehner and other Republicans accuse the administration of misleading the American people after the attack to protect Obama in the final weeks of his re-election campaign, and of stonewalling congressional investigators ever since. They pointed to emails released only last week as further evidence of White House wrongdoing.

Rep. Steny Hoyer of Maryland, the No. 2-ranked Democrat, said he and his colleagues would first have to see the specifics of Boehner’s proposed committee before making a decision on participating in or boycotting the new probe. He said he and other party leaders would vote against establishing the committee.

“This has been seriously and thoroughly investigated,” said Hoyer, citing 13 public hearings on the Benghazi attack, 25,000 pages of documents handed over and 50 separate briefings. “There was nothing the military could have done in the time-frame available,” he told reporters Monday. He said all investigations thus far have produced “no smoking gun, no wrongdoing.”

Republicans have pointed a finger at one passage in particular among the 40 or so emails obtained last week by the watchdog group Judicial Watch through a Freedom of Information Act request. Three days after the attack, Ben Rhodes, then the deputy national security adviser for strategic communications at the White House, stressed the goal of underscoring “that these protests are rooted in an Internet video, and not a broader policy failure.”

The email was written the Friday before then-U.N. Ambassador Susan Rice appeared on the Sunday television news programs and explained the Benghazi attack as a protest over a YouTube video that mocked the Islamic prophet Mohammed that was hijacked by extremists. Administration officials later changed their description of the attack and said references to a protest were inaccurate.

Asked if Rhodes’ email constituted proof of administration wrongdoing, Hoyer said: “That’s baloney.” He said the memo largely mirrored CIA language and joked that it must be shocking that administration officials receive suggestions on what they’ll say before they appear on national news programs. “I was astounded that any White House would do that,” he said.

However, Hoyer left open the small possibility of Democratic involvement in the select panel. He said it “ought to be an equally balanced committee, so that this is not an exercise in partisanship. We’ll see whether that’s the case.”

In 2005, most Democrats boycotted a Republican-led select committee examining the Bush administration’s response to Hurricane Katrina. Democrats had sought an independent investigation.

Establishment of the select committee is almost a formality given the GOP’s control of the House. Democrats controlling the Senate have shown no interest in launching a similar probe.

“With four of our countrymen killed at the hands of terrorists, the American people want answers, accountability and justice,” Boehner said Monday in a statement.

He called Gowdy, a former prosecutor in his second term in Congress, “as dogged, focused and serious-minded as they come.”

The committee will have “the strongest authority possible to root out all the facts,” Boehner said.

Separately, the State Department said Monday that Secretary of State John Kerry would not appear before the House Oversight Committee on May 21 to talk about Benghazi — as demanded in a subpoena from the panel’s chairman, Rep. Darrell Issa, R-Calif.

Department spokeswoman Marie Harf said Kerry planned to travel to Mexico at that time and officials would discuss alternative options with the committee.